The present invention relates to disc or butterfly type valves in which a disc is pivotally disposed within a conduit of the valve defined by a generally cylindrical housing for pivotal movement of the disc between an open position, in which it is generally parallel to an axis of the valve, and a closed position in which the disc is generally perpendicular to the valve axis.
Disc valves as such are presently in wide use. The specific construction of such valves differs widely. One advantageous construction is disclosed and claimed in U.S. Pat. No. 3,442,488. The valve disclosed in that patent includes a disc fitted with a peripheral seal ring and rotatable about an eccentric axis for moving the seal ring into and away from sealing engagement with an internal sealing surface of an annular valve seat defined by the housing of the valve. The sealing surface is a conical surface whose axis forms an acute angle with the axis of the valve housing. An improvement to such a valve and in particular to the construction, alignment and operation of the sealing ring carried by its disc is disclosed in U.S. Pat. No. 4,003,394.
The valves disclosed in the above-referenced U.S. patents have yielded excellent operating results, that is they assure air tight seals under the most adverse operating conditions such as high fluid pressures and/or temperatures, high flow rates, the handling of chemically or mechanically abrasive fluids, etc., and they have enjoyed a corresponding commercial success. It is believed that the technological efficiency of such valves is at least in part the result of the particular sealing arrangement employed by them, especially the provision of an angularly offset (with respect to the valve axis) but otherwise conical seating surface in the valve housing and a correspondingly arranged seal ring in the disc which assured that the latter is wedged into sealing engagement with the former when the disc is tilted into its closed position. The wear of the seating surface and/or of the seal ring from predominantly sliding engagement is thereby reduced or eliminated.
This advantageous operating characteristic of the valve, however, complicated its manufacture and required, for example, special jigs, tools, and machinery to accurately machine the angularly offset, conically shaped seating surface in the housing. This is particularly true for valves of relatively large diameter, say in the order of 24 inches or more where the cost of such jigs, tools, etc, can be a significant factor in the overall cost of the finished valve. Similar care had to be exercised in manufacturing the disc and the seal ring mounted therein. Thus such valves are not always as economical to manufacture as may be desired.
On the other hand, attempts to build disc valves with conical seal rings and seats that are coaxial with the valve axis have met only limited success. Although such constructions can sometimes be effective for low pressure, particularly in instances in which a perfect seal is not required, they have generally been ineffective for establishing air tight seals under adverse operating conditions since even the slightest degree of eccentricity can cause the loss of the seal. Further, such arrangements are effectively limited to disc valves in which the disc acts as a flap e.g., in which the disc is pivoted about a pivot axis that is located outside the seal ring diameter. Since such arrangements require a high operating torque for opening the disc against fluid pressure, they are only feasible for low pressure applications.